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Abstract

Some technical applications require a fully reversible fan. That means that the fan performance characteristics must be identical for both flow directions. Several design principles are known for both, centrifugal and axial fans. The objective of this paper is the design, manufacture and test of a small fully reversible axial fan.
The design chosen consists of two identical contra-rotating impellers without guide vanes, placed in mirror image to each other in a duct-type housing. The blades of the impellers are made of thin non-cambered airfoil elements of constant thickness, fully symmetric to the stagger line. Stagger angle and solidity of the blade cascade as function of the radius are optimized for maximum performance. Each impeller is operated by a separate motor with individual continuously variable speed. Of interest is the field of characteristic performance curves as a function of the impeller speed ratio.
Two 80 mm diameter impellers are designed and manufactured via 3D printing. Impellers and the electronically commutated motors are mounted in a precision aluminum tube via three circular struts.
The volume flow rate/total-to static pressure rise and efficiency characteristics are measured for several speed ratios. As targeted, one distinct speed ratio provides an exit flow without swirl, i.e. fan performance with maximum total-to-static efficiency. As an outlook several of these contra-rotating impeller assemblies could be placed in one duct without guide vanes in order to increase the pressure rise of the unit while maintaining full reversibility.